Automatic Dependent Surveillance-Broadcast, or ADS-B, is a cooperative surveillance technology in which an aircraft periodically broadcasts its position, velocity, and flight identification, allowing for the aircraft to be tracked. This periodic broadcast is typically referred to as “ADS-B Out”. The information can be received by air traffic control ground stations, and can also be received by other aircraft to provide situational awareness and allow self separation. The receipt of another aircraft's broadcast is typically referred to as “ADS-B In”.
The ADS-B Out function is usually performed by an onboard transponder. A transponder (short for transmitter-responder, and sometimes abbreviated to XPDR) is an electronic device that produces a response when it receives a radio-frequency interrogation. Other systems onboard the aircraft, such as traffic collision avoidance system (TCAS) or the like, may also use the transponder as a means of detecting aircraft at risk of colliding with each other.
The addition of the ADS-B Out function to the transponder brought with it the requirement to have an ADS-B Out function failure annunciation and an ADS-B Out device failure annunciation. As the ADS-B Out function is within the transponder, the ADS-B Out device failure requirement is fulfilled by an existing transponder failure indication where the transponder may self report when a failure is experienced.
There are two methods by which the ADS-B Out function failure may be indicated. One method is the addition of a new failure annunciation in the cockpit. Due to the expense of adding new indications, this method is not preferred for many existing aircraft installations. The other method is to combine the ADS-B Out function failure with the transponder failure, provided that a user (e.g., a pilot) can determine which failure is present.
Currently, when a failure occurs, an indicator is provided to notify a user (e.g., a pilot) of the failure. However with a combined transponder/ADS-B Out failure indication, the indicator does not specify whether the failure was caused by a transponder failure or an ADS-B Out function failure. In order to determine the source of the failure, the user may need to observe if another system using the transponder (e.g., the TCAS) is also failed. If the TCAS still functions properly, it may suggest that the transponder also functions properly, and the user may determine the source of the failure to be an ADS-B Out function failure. On the other hand, if the TCAS fails to function properly, the user may determine the source of the failure to be a transponder failure.
It is noted, however, that this determination can be misleading in some cases. For instance, if the TCAS has failed for another reason (such as the lack of a valid radio altitude input) instead of a failed transponder, the user may incorrectly conclude that the failure was caused by the transponder using the current test procedure. Therein lies a need for systems and methods for distinguishing ADS-B function failures from transponder failures without the aforementioned shortcomings.